The present invention relates to an endoscope having an operation section and an insertion section, and more particularly to an endoscope having a flexible fiber optic conduit coupled at one end to the proximal end of an operation section and at the other end to the distal end of an insertion section.
2. Description of the Prior Art
A typical endoscope comprises an insertion section and an operation section. It further comprises a guide fiber having, for example, an image guide fiber or a light guide fiber, and extending from the operation section to the distal end of the insertion section. One end of the guide fiber is fastened to the proximal end of the operation section, and the other end thereof is secured to the distal end of the insertion section. The guide fiber is made of a number of quartz glass element fibers. The element fibers are bonded together by filling the gaps among them with molten cladding agent. Were the element fibers not bonded, the periphery of each fiber should be coated with a lubricant layer, thereby to prevent the wear of the individual element fibers. Were element fibers coated with lubricant layers, the guide fiber as a whole should have a large outer diameter. Therefore, the molten cladding agent is filled in the gaps among the element fibers, thereby forming a so-called "conduit-type" guide fiber having a small outer diameter. Since the guide fiber of this type is used in the endoscope, the insertion section thereof can have a small diameter.
However, the guide fiber of the conduit type is rigid. When it is used in an endoscope, with its both ends fixed, the insertion section of the endoscope inevitably becomes less flexible. Further, the conduit-type guide fiber may be broken when the insertion section is bent excessively.
Japanese Patent Disclosure (Kokai) No. 58-1905 discloses an endoscope designed to solve these problems with a conduit-type guide fiber. In this endoscope, one end of the conduit-type guide fiber, or a rigid, image guide fiber, is fastened to a holder holding an objective lens, and the other end of the fiber is slidably supported by a holder holding an ocular lens. Since the other end of the fiber can slide with respect to the ocular holder, no bending stress is exerted on the fiber when the insertion section is bent. When the other end of the fiber slides, however, the distance between this end of the fiber and the ocular lens changes. Consequently, the image of the interior of the body cavity, which is being examined through the endoscope, comes out of focus. Moreover, when the image guide fiber is combined with a light guide fiber, the amount of light input to the light guide fiber inevitably changes as the end of the image guide fiber slides with respect to the ocular holder.